Protip, as @ben_lubar noted, you really want to look at Babelmark when testing Markdown quirks. The language (and I use that term loosely) does not really have an unambiguous spec. It is something that John MacFarlane is working on currently @sam so you should just email him if you want it to happen faster. No reason to do anything other than that at this time.

I don't think that's a battle we need to fight right now. If you want maximum benefit from your actions, work with John MacFarlane on the official Markdown Next spec. That is the best course of action versus Yet Another Parser That Interprets an Ambiguous Spec a Certain way.

Markdown does not even have a proper spec and by proper I mean one that can be implemented without ambiguity. Turns out, John Gruber is... kind of a shitty computer scientist, which may come as a surprise to no one.

So in this case there is no standard, just differing interpretations of an inherently ambiguous spec.

Nobody seems to complain that each forum software has its own interpretation of bbcode. Provided the very simplest stuff is consistent, no-one will complain if you have different Markdown for the most complex stuff mostly because almost no-one will use it anyway (lack of discoverability, lack of need etc.)

The fact you have three separate routes for content entry which are clearly conflicting with each other is also really not helping your case.

If you don't like the Markdown spec, don't use it. Write your own. You're already determined to reinvent the forum as we know it, why not go one step further and reinvent Markdown?

Or drop Markdown and use bbcode. Trying to be all things to all people is a headache you've made for yourself.